In recent years, with the rapid development of display technology, thin film transistor used to drive and control a pixel of a display device has been developed as well, and has been developed from amorphous silicon thin film transistor and low temperature poly-Si thin film transistor to oxide thin film transistor.
The oxide thin film transistor has excellent characteristics in electron mobility, on-state current, switching performance and so on. In addition, the oxide thin film transistor further has advantages of few non-uniform device characteristics, low cost, low process temperature, capable of employing a coating process, high transmittance, large band gap and so on. The oxide thin film transistor can be used to the display device requiring fast response and large current, such as a liquid crystal display with high frequency, high resolution or large size, organic light emitting display and so on.
FIG. 1 is a cross-section schematic view illustrating a conventional oxide thin film transistor. As shown in FIG. 1, the conventional oxide thin film transistor comprises a substrate 1, a gate electrode 2, a gate insulation layer 3, an active layer 4, ohmic contact layers 5a and 5b, an etching barrier layer 6, a source electrode 7a and a drain electrode 7b. The ohmic contact layers 5a and 5b are formed by using the following process: firstly depositing an oxide thin film having better conductivity than the active layer on the active layer, and then forming the ohmic contact layers by an etching process. By forming the ohmic contact layers 5a and 5b, the schottky effect between the source and drain electrodes and the active layer can be reduced, and the contact property between the source and drain electrodes and the active layer can be improved.
However, the active layer and the ohmic contact layers in the oxide thin film transistor are all formed by oxide material, and it is difficult to control the etching process for etching the oxide thin film to form the ohmic contact layer by using an etching solution, and the etching solution is very likely to damage the oxide active layer.